1. Field of the Invention
The invention relates generally to an air induction system for a motor vehicle. More specifically, the invention relates to a noise attenuation device positioned within an air induction system.
2. Related Technology
As is known in the art, an air induction system supplies air to one or more combustion chambers in a vehicle engine. The variable-volume of each of the combustion chambers is controlled by an actuating piston within a combustion chamber cylinder. As the piston actuates in a downward direction (known as the downstroke) ambient air is drawn through the air induction system and into the combustion chamber for mixture with fuel vapor. The piston then actuates in an upward direction (known as the upstroke) and compresses the fuel-air mixture. Next, a spark plug ignites the compressed fuel-air mixture and causes the piston to move downwardly, thereby generating a work output for the motor vehicle.
Air induction systems typically include an air filter assembly to remove dirt and other particulates from the incoming air flow and to prevent such particulates from entering the combustion chamber. The air filter assembly typically includes a housing defining a chamber and an air filter located within the chamber. As the air flow is caused to flow through the air filter, particulates are trapped and removed from the airflow.
Air induction systems sometimes also include a turbocharger to provide a boost in the work output. More specifically, turbochargers are positioned in the air induction system, between the air filter assembly and the combustion chamber, to compress the ambient air. Due to its compressed state, the air is able to be mixed with an increased amount of fuel vapor, thereby increasing the maximum potential work output of the compression chamber. Typically, turbochargers include a rotating turbine that draws air towards the engine at an increased pressure.
The air stream entering the air induction system often causes the vehicle occupants to experience an increased noise, vibration, and harshness (NVH) level. More specifically, the actuating of cylinders causes pulses of air to be drawn into the air filter chamber, thereby increasing the NVH levels in the air induction system. Furthermore, vehicles that include turbochargers are especially susceptible to increased NVH levels due to the rotating compressor blades and the pressure pulsations they produce.
To reduce the NVH level within the vehicle, currently-known air induction systems therefore sometimes include a noise attenuation device. More specifically, these attenuation devices, known as sidebranch resonators, typically include a relatively large volume of stagnant air and a passageway having a relatively small area connecting the air intake conduit to the volume of stagnant air. For example, in one construction the passageway extends through the conduit housing in a direction transverse to the main airflow direction along the conduit. The volume of stagnant air is contained within a separate structure, such as a sleeve surrounding the conduit and cooperating with the conduit's outer surface to form a ring-shaped space, or a self-containing housing such as a sphere, of stagnant air that is connected to the passageway. During operation of the sidebranch resonators, air contained within the passageway resonates back and forth between the volume of stagnant air and the conduit, thereby attenuating noise within the conduit at a specific frequency.
This design however, requires additional components to define the volume of stagnant air, thereby requiring additional material costs and having a more bulky design. Therefore, the sidebranch resonators may not be able to be packaged in the underhood space and may be cost prohibitive.
In another currently-known design, a plurality of hollow fins are included in the conduit containing a volume of stagnant air and a number of “holes” that communicate with the conduit thereby reducing NVH levels in the same manner as the sidebranch resonator. However, similar to the sidebranch resonators, this design requires additional components and may be cost prohibitive to vehicle manufacturers. Furthermore, the fins may restrict airflow through the conduit.
It is therefore desirous to provide an air induction system with a noise attenuation device that substantially reduces the NVH levels experienced by the vehicle occupants, a simple construction and a generally compact design.